Properties and Hydration Mechanism of Cementitious Materials Prepared from Calcined Coal Gangue

Abstract

The preparation of cementitious materials by replacing part of the cement with activated coal gangue is of great significance to the cement industry in terms of carbon reduction and coal-based solid waste utilization. For this paper, cementitious material was prepared by firing activated coal gangue under suspension conditions and batching it with limestone powder using Inner Mongolia coal gangue as raw material. The optimal ratio was determined by testing the strength changes of the cementitious material at 3, 7, and 28 days of hydration, and the hydration process and mechanism were explored by combining the pore structure, heat of hydration, chemical composition, phase composition, and microscopic morphological characteristics of the hydration products. The results showed that the active materials formulated from activated gangue and limestone powder can be used to prepare cementitious materials with good performance at the level of 30%–50% replacement of cement. The optimal ratio was 30% replacement of cement, and the mass ratio of calcined gangue to limestone powder was 2:1. The 3 days compressive strength of this ratio was 28.8 MPa, which was only slightly lower than that of cement. However, the 28 days compressive strength of samples reached 67.5 MPa, which was much higher than that of the reference cement. In the hydration of this cementitious material, not only does the activated coal gangue react with the Ca(OH)2 formed by hydration to form C–S–H gel, but CaCO3 also participates in the reaction to form a new phase of carbon aluminate, and the two effects together promote the development of the later strength of the samples. This paper can provide a reference for carbon reduction in the cement production process and comprehensive utilization of coal gangue.